The developmental stage of the shoot apical meristem affects the response of Lilium candidum bulbs to low temperature

Abstract

Madonna lily (Lilium candidum) is a flowering geophyte growing wild in Israel and in the neighboring region. In view of its holly character in the Christian culture, L. candidum has a great commercial potential as an ornamental crop. However, knowledge regarding its cultivation and the control of its flowering time is very limited.In this study, we aimed to define external factors affecting L. candidum flowering and characterized the developmental stages of the shoot apical meristem (SAM), under different temperature and photoperiod regimes. We found that in most cases, bulb or plant exposure to low temperature (4 °C, forcing) hastened floral transition and flowering in a quantitative manner, whereas day length had a negligible effect on these traits. These results suggest that vernalization is a major pathway regulating flowering time in L. candidum. We also characterized a novel phenomenon in which exposure of the bulb to low temperature led to a delay in bolting and flowering until the following season. We showed that the ability of a bulb to perceive cold exposure as signal for flowering hastening or as a delay was dependent on the SAM's developmental stage and was related to the season. During the summer, cold exposure applied to the SAM at the juvenile phase results in growth inhibition, while from the fall onward, when the meristem has reached its vegetative adult phase, cold exposure promotes bolting and flowering, according to the classic vernalization response. Exposure of the juvenile bulb to 12 °C promotes the transition of the SAM from juvenile to vegetative adult.In conclusion, we showed cold exposure of bulbs at the juvenile phase induced the inhibition of the bolting and flowering, while bulb cold exposure of bulbs at the vegetative adult stage promoted flowering. This study sheds light on the development and flowering physiology of L. candidum and can have applied outcomes for its cultivation as a cut flower crop.